Is the James Webb Space Telescope (JWST)capable of seeing galaxies over the universe’s horizon?

Since it started sending data back to Earth in 2022, JWST has significantly impacted astronomy, and one of its most revolutionary accomplishments is the observation of some of the most distant galaxies ever seen. But, because light doesn’t travel instantly — but rather travels at about 300 million meters (985 million feet) per second in a vacuum — we don’t see those galaxies as they are now, but as they were billions of years ago.

Moreover, our cosmos is estimated to be 13.8 billion years old. So, we should assume that the most far away galaxy we could ever hope to see is no more than 13.8 billion light-years away. (One light-years is the distance light covers in a year). That point ostensibly should be a “cosmological horizon” of sorts — beyond which no telescope should be in any way able to see. And, as nothing can travel through space faster than c, that means there should be absolutely no way a galaxy further than 13.8 billion light years away, and getting more distant continually could affect Earth. Right?

Wrong. If only the cosmos were that simple.

“A cosmological horizon is a maximum distance from which one could possibly retrieve information,” Jake Helton (a University of Arizona astronomer who is also part of the JWST Advanced Deep Extragalactic Survey team) told Space.com. Helton added, “There are a few different cosmological horizons which have different definitions and depend on various cosmological quantities. The most relevant here is the cosmological horizon which is the maximum distance from which light could have traveled to us in the age of the universe. This definesthe edge of the observable cosmos.”

In March of 2024, the JWST Advanced Deep Extragalactic Survey (JADES) scientists disclosedthat the powerful telescope had spotted JADES-GS-z14-0, the most far away and early galaxy humanity has ever seen. The absurdity, however, is that JADES-GS-z14-0 is located about 33.8 billion light years away.

How on earth can we see light from an object so distant the cosmos isn’t old enough to have permitted it to have reached us? Doesn’t JADES-GS-z14-0’s placement 33.8 billion light-years away mean we see it as it was 33.8 billion years ago, something that would certainly challenge the estimation of the age of the cosmos?

Not so. Again, this is evidence that the cosmos has a way of turning logical and sensible conclusions on their heads.

“How can a distant galaxy like JADES-GS-z14-0 ever be observed, since it is more than 13.8 billion light years away from us and its light seemingly would have taken more time than the age of the universe to reach us?” Helton enquired rhetorically. “The answer is the expansion of the universe.”

Seeing a galaxy older than time itself

If the cosmos would just sit still, then light from a galaxy 33.8 billion light-years from the earth would take 33.8 billion years to reach us, and that would be that. But, in the early 1900s itself, Edwin Hubble discovered that distant galaxies appeared to be receding away from each other, and the further apart they were, the quicker they were going. In other words, the cosmos isn’t static; it is expanding.

This was further convoluted in 1998, as the 20th century was about to end two separate teams of astronomers observed that, not only is the cosmos expanding, but that expansion is also in fact accelerating. The force responsible is an enigma, but it has been given the name of “dark energy.”

There are two main and distinct periods of expansion over the 13.8 billion-year history of the cosmos. The first is an initial epoch of rapid cosmic inflation that is now commonly termed the “Big Bang.” This inflationary period saw the volume of the cosmos increase by a factor of 10^26 (10 followed by 25 zeroes).

This was followed by a matter-dominated period beginning 47,000 years post the Big Bang. Eventually, universal expansion permitted the universe to cool enough to allow protons to form from quarks and gluons, and subsequently protons to bond with electrons to form the first atoms of hydrogen, which formed the initial stars and galaxies. During this epoch, the Big-Bang-driven expansion of the cosmos slowed to a near halt.

The matter-dominated epoch came to an astounding end when the cosmos was just under 10 billion years old. At this time, the cosmos suddenly began to expand rapidly yet again. Additionally, that expansion got quicker and quicker and continues to accelerate even today. This third significant epoch of the universe is termed the dark-energy-dominated period. It’s the period we’re currently in.

By virtue of these periods of expansion of the cosmos, the light from JADES-GS-z14-0 has actually been traveling to the JWST and Earth for 13.5 billion years, notwithstanding its source now being far more distant than 13.5 billion light-years away. That means the JWST sees JADES-GS-z14-0 as it was 300 million years post the Big Bang. Without the expansion of the cosmos, JADES-GS-z14-0 would still be about 13.5 billion light-years away, though it would have still very well experienced smaller local motions that could have moved it closer together or further from proximate galaxies. But such galactic movement would’ve been nothing compared to the kind caused by the expansion of the universe.

According to Helton, the cosmological horizon is a sphere with a frontier around 46.1 billion light years away, a figure dictated by the cosmos’s expansion. This is the actual horizon beyond which we should be unable to “see” a galaxy. The galaxy JADES-GS-z14-0 is in fact within that horizon.